Toxicity of Metarhizium anisopliae (Metchnikoff) Sorokin strain ESC-1 with and without selected insecticides to control German cockroach, Blattella germanica (L.)
Metarhizium anisopliae (Metchnikoff) Sorokin strain ESC-1 was virulent to German cockroach, Blattella germanica (L.). Topical application of M. anisopliae strain ESC-1 resulted in mortality ranging from 31.3 to 86.3% in 21 d. The lethal dose (LD 50) of M. anisopliae strain ESC-1 estimated for German cockroaches was 4.18 × 108 spores per milliliter. In vitro compatibility studies between insecticides plus M. anisopliae indicated compatibility with most of the insecticide concentrations used. There was no significant difference in the germination of conidia cultured on insecticide-amended SDAY media. But colony growth and sporulation was significantly affected by incorporation of insecticide to SDAY media. Colony growth was partially inhibited at 50 and 500 ppm of chlorpyrifos, and 500 ppm of propetamphos. There was no sporulation at 500 ppm of chlorpyrifos and propetamphos, and sporulation was significantly affected at 50 ppm of chlorpyrifos. Both additive and synergistic effects were observed in the in vivo compatibility study illustrating compatibility between the two agents. In general, joint application of insecticide plus M. anisopliae resulted in an additive effect. The only exception was 300 ppm of propetamphos where a synergistic effect was observed. Lethal time was significantly reduced in many of the insecticides plus M. anisopliae combinations by 50% or greater than half fold differences compared with M. anisopliae alone. Metarhizium anisopliae, insecticides, and insecticide plus M. anisopliae combinations did not affect the body weight of German cockroaches. There was no detectable level of destruxins identified from the culture filtrate of M. anisopliae strain ESC-1. Bioassay with destruxins by itself or in combination with sublethal doses of insecticides did not significantly increase mortality in German cockroaches
